Is there any way to predict a woman's reproductive lifespan?

These days, it's hard to open a magazine without reading about some novel development in infertility medicine: A doctor performs transplants of the uterus (albeit in mice); couples pay to choose the sex of their baby. But most of the wizardry of infertility technology—such as in vitro fertilization, the formerly revolutionary, now quotidian procedure in which egg and sperm are merged in a Petri dish, and the resulting embryos transferred to the woman's uterus—has, understandably, been focused on helping those who are having trouble getting pregnant to do so.

Yet as one of the millions of women who are now, by choice or circumstance, postponingpregnancy, I became curious: If you're a woman who's not yet trying to conceive, but may someday want to, is there any way to know your future fertility?

Right now, the answer is no. While this might seem surprising, it isn't so odd when considered in the context of the fertility business. Fertility clinicians, after all, are trained to diagnose and treat existing fertility problems—not to screen for future ones. And if the great majority of their patients want to be pregnant yesterday—and will pay high sums to be so—why should they take time to conduct highly experimental research for those who might want to be pregnant tomorrow?

As it happens, a few fertility researchers are now taking the time. Teams at Erasmus Medical Center and Utrecht University—both in the Netherlands—and (if funding comes through) at the University of California at San Francisco, are now, or will soon be, investigating methods that might one day be used to predict a woman's reproductive lifespan and answer that anxiety-inducing question that plagues so many women today: How many fertile years do I have left?

As we've all heard, fertility declines with age: By the time a woman reaches her late 20s, it may take a little longer for her to conceive; by her mid-to-late 30s, it can become dramatically more difficult. And by her early 40s, harder still.

Of course, these are only population averages; reproductive lifespan differs wildly among women. But how to identify individual women who are potentially at risk for an early end to fertility? Perhaps, researchers say, via methods used now to diagnose and treat infertility.

For all women, the general decline in fertility that comes with age seems to stem in good part from the decline in what's called "ovarian reserve"—the quality and quantity of a woman's eggs. A woman is born with a finite number of eggs; over time, her supply dwindles, due to what doctors call "ovarian aging."

Today, infertility clinicians often infer a woman's ovarian reserve by measuring blood levels of a host of reproductive hormones. This is done in order to predict her short-term odds of success with ovulation-inducing drugs used in infertility treatments. The hormones linked to ovarian reserve include follicle-stimulating hormone (or FSH), along with lesser-knowns such as inhibin B and antimullerian hormone. High blood levels of FSH on specific days of the menstrual cycle may indicate that there has already been a decline in egg quality and quantity. Low levels of inhibin B on these days may also indicate a similar signal of a decline, as may low levels of antimullerian hormone.

An alternate method of assessing ovarian viability is using an ultrasound to observe the numbers of antral (or developing) follicles in the ovaries. During each menstrual cycle, a certain number of egg-containing follicles will reach this antral stage. Researchers hypothesize that the higher the antral follicle count, the better the odds are that a woman can get pregnant.

Some doctors already offer antral follicle counts or FSH tests to women not yet trying to conceive in order to provide a sense of their current—not future—ovarian reserve. But there is much to learn before such methods can be applied with full confidence to women in the general population. For one thing, most studies investigating these methods have thus far been done on women undergoing infertility treatments, who may not respond to the tests in ways identical to women in the general population. For another, most of the studies have not tracked women over the long haul.